FSTC 326 Chapter Notes - Chapter 27: Ice Crystals, Ionic Strength, Supercooling
4 Nov 2016
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Cool storage refers to storage at temperatures from about 16 to -2 c. Refrigeration temperature = below minimal growth temperature of most foodborne microbes. Refrigerated foods can also spoil rapidly if their initial microbial populations are high. Temperature range over which an organisms can grow depends on its ability to regulate membrane fluidity. At low temps = psychrotrophs have more unsaturated fatty acid residues and more branched-chain fatty acids in their lipids. Leads to decrease in lipid melting point aka increased fluidity. Homeoviscous adaptation = the idea that cells alter their fatty acid compositions to maintain membrane fluidity. Totally frozen state = -15 to -20 for fruits and vegeables and below -40 c for meats. Concentration of cellular liquids changes the ph and ionic strength. This inactivates enzymes, denatures proteins, and inhibits metabolic processes. Injury of microbial cells may be reversible or irreversible. Freezing rate has major impact on microbial viability. Cell"s cytoplasm becomes supercooled at -5 to -10 c.
